Consider the following activities: 1. Spreading finely ground basalt rock on farmlands extensively 2. Increasing the alkalinity of oceans by adding lime 3. Capturing carbon dioxide from industries and pumping it into abandoned subterranean mines as carbonated water. How many of these are often discussed for carbon capture and sequestration?

All three. All three activities are genuinely discussed as carbon capture and sequestration methods: enhanced weathering with basalt, ocean alkalinity enhancement, and mineral carbonation in mines. Read more: EnvEco0199 - Carbon Capture Methods: Basalt, Ocean Alkalinity, and Mine Injection.

Why does adding lime to increase ocean alkalinity help capture atmospheric carbon dioxide?

It enhances the ocean's natural capacity to absorb CO2 from the air. Adding lime raises ocean alkalinity, which enhances the ocean's natural capacity to absorb carbon dioxide from the atmosphere. Read more: EnvEco0199 - Carbon Capture Methods: Basalt, Ocean Alkalinity, and Mine Injection.

Carbon Capture Methods: Basalt, Ocean Alkalinity, and Mine Injection

Carbon capture means pulling CO₂ from air or exhaust. Storage keeps it out of the air for a long time. Basalt, ocean alkalinity and mine injection are three different paths.

Basalt columns on the Isle of Staffa. Finely ground basalt is spread on farmland as a carbon capture technique. Photo by RichTea, CC BY-SA 2.0, via Wikimedia Commons.

At a Glance

Four facts to hold on to.

Basalt

Ground rock weathers and binds CO₂.

Ocean alkalinity

Alkaline material helps seawater hold more carbon.

Mine injection

Carbonated water reacts in suitable rock.

UPSC 2023

All three are discussed.

AlkalinityWater’s ability to resist turning acidic.

MineralisationCO₂ turning into solid carbonate rock.

MRVMeasuring, reporting and verifying removal.

Enhanced weatheringSpeeding up natural rock weathering.

In this lesson

Three Different Paths
How Each One Works
Evidence and Limits
Previous Year Questions

Three Different Paths

Must Know

Capture, removal and storage

Capturing factory CO₂ prevents part of an emission. It does not remove older CO₂ from the air.
Carbon dioxide removal takes CO₂ already in the air and stores it for long.
Storage can be underground, in minerals or in ocean chemistry.
Energy use, transport and leaks can shrink the benefit. Count the whole chain.
Sources: IPCC AR6, removal methods; IEA, capture and storage.

Three methods compared

Method	CO₂ source	Path	Evidence
Crushed basalt on land	Air	Weathering makes bicarbonate and sometimes carbonate	Trials; net removal is hard to measure
Ocean alkalinity	Air	Seawater holds more dissolved carbon	Research and pilots
Carbonated-water injection	Captured CO₂	Suitable rock mineralises it	Basalt pilots exist

An abandoned mine is not automatically a safe store.

True or False: Spreading finely ground basalt may remove atmospheric CO₂ through faster weathering.

How Each One Works

Good to Know

Basalt on farmland

Basalt is a volcanic rock rich in reactive minerals.
Grinding it gives rain and soil water more surface to act on.
Weathering can turn CO₂ into dissolved bicarbonate. Rivers may carry it to the sea.
Some carbon becomes solid carbonate. Not every grain turns to stone at once.
Mining, crushing and spreading use energy. Trace metals need checking.
Source: IPCC on enhanced weathering.

Raising ocean alkalinity

Adding alkaline material changes seawater chemistry.
That may let the ocean take up more CO₂. The carbon stays mostly in dissolved forms.
The exam mentions lime. Making lime releases CO₂ and needs much heat.
Local pH change and effects on sea life need testing.
NOAA calls this an emerging research area. It is not a proven worldwide fix.
Source: NOAA, marine carbon removal.

Carbonated water underground

A plant first separates CO₂. Operators dissolve it in water and send it down a well.
In suitable basalt, the CO₂ reacts with calcium or magnesium and forms solid carbonate.
This differs from storing compressed CO₂ under a cap rock.
Old mines have shafts, fractures and wells. These can leak.
Engineers must test rock, seals, water flow and nearby drinking water.
Sources: US NETL, storage FAQs; US DOE, geological storage.

True or False: Every grain of field-spread basalt instantly becomes a solid carbonate mineral.

Evidence and Limits

Great to Know

What CarbFix showed

CarbFix injected CO₂ dissolved in water into Icelandic basalt.
A 2016 paper reported over 95% mineralised within two years.
That was a measured pilot at a suitable site. It does not prove every rock layer or mine works.
Source: Matter and colleagues, 2016 pilot study.

How to prove a benefit

MRV means checking how much CO₂ was truly removed or stored.
A basalt field needs a baseline and soil and water measurements.
An ocean trial needs background seawater readings. Currents can move the signal.
An injection project tracks the well, underground movement, pressure and water.
A certificate is not proof by itself.
No method removes the need to cut new fossil-fuel emissions.
Sources: IPCC; NOAA; IEA.

Think it through: why can an abandoned mine not be assumed to store CO₂ safely?

The mine may have shafts, fractures and old wells. CO₂ or changed groundwater could escape. Engineers must test the site and keep monitoring it.

True or False: The 2016 CarbFix pilot reported over 95% of injected CO₂ mineralised within two years.

True or False: An abandoned underground mine is automatically a safe CO₂ store because it has empty space.

Exam Edge

Previous Year Questions

UPSC 2023 asked about three carbon-capture ideas.

UPSC 2023, Q68Which of these are considered for carbon capture and sequestration: (1) spreading ground basalt on farmland, (2) raising ocean alkalinity with lime, (3) pumping captured CO₂ into abandoned subsurface mines? The answer is (c), all three. The wording does not mean each is ready at scale. View the question.

True or False: UPSC 2023 listed basalt spreading, ocean alkalinity and mine injection as carbon-capture ideas under discussion.

Quick Q&A

Basalt route?

Weathering makes bicarbonate.

Lime risk?

Making lime emits CO₂.

CarbFix result?

Over 95% in two years.

Old mines?

Not automatically safe.

UPSC 2023 answer?

All three.

0 / 5 correct

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